An adhesive stick is a solid mass of adhesive which is used to transfer pressure sensitive adhesive to a substrate by rubbing the stick across the substrate. Adhesive sticks have been designed both for hand-held use and for adhesive transfer by machine. Adhesive sticks provide a simple alternative means of adhesive transfer wherein extraneous equipment such as heating equipment needed for hot melt adhesives or radiation sources needed for radiation curable adhesives are not required. However, existing adhesive sticks have practical drawbacks.
U.S. Pat. Nos. 4,639,475; 3,846,363; 3,929,694; and 3,576,776 disclose adhesive stick compositions. But the disclosed adhesive compositions must be stored in containers or special packaging to prevent the evaporation of volatiles. Prolonged exposure to air would cause adhesive compositions containing volatiles to decompose and become too dry and brittle to be useful. Air instability of adhesive sticks is especially problematic for adhesive sticks designed for hand-held use by the general public. Children are especially prone to leaving such art supplies uncapped or otherwise exposed for long periods.
U.S. Pat. No. 5,331,023 claims an adhesive stick composition containing a blend of polyisobutylene and a wax. The disclosed composition does not contain volatiles and is stable in air. However, the viscosity of the polyisobutylene raw material is about 15,300 to 46,000 centipoise. The use of a raw material having such high viscosity presents manufacturing difficulties.
The adhesive sticks disclosed in U.S. Pat. Nos. 3,539,481; 3,267,052; 3,267,052; 3,539,481; and 5,331,023 require significant frictional rubbing action of the stick across a substrate to cause the adhesive to be delivered in a satisfactory manner. These adhesive sticks are difficult to use due to their hardness.
In light of the above, it would be desirable to have a solid adhesive composition which is easily processable, stable in air, strong enough to withstand the force required for it's use, soft enough to readily transfer adhesive to a substrate, and having an adequate amount of bonding strength for usefulness on a variety of substrates.